Reinforced graft

ABSTRACT

A graft is provided with a flexible sheet of graft material to which is sewn a reinforcing wire, preferably of shape-memory alloy. Sewing of the wire is carried out while the sheet is substantially planar, thus by conventional embroidery machines. The sheet is subsequently rolled into a tubular shape.

FIELD OF THE INVENTION

This invention relates to a reinforced graft and to a method ofproducing such a graft which may be used for the treatment of aneurysms,eg in the aorta, by an endoluminal technique, which is minimallyinvasive and which can therefore be used on many patients who are tooold or frail to be able to withstand conventional surgery.

BACKGROUND OF THE INVENTION

Conventional vascular grafts commonly consist of a textile or polymertube which is implanted into a patient in a major open surgicalprocedure, grafts which have been implanted endoluminally, that is fromwithin the vessel, consist of grafts which are combined with stents.Such grafts are very time-consuming to produce and this causesparticular problems when a bespoke graft is required to be produced atshort notice.

Additionally, one of the major problems of existing vascular grafts forendoluminal surgery is that, because of the tortuous bends commonlyencountered between the aorta and iliac arteries of patients withaneurysms, there is a tendency for existing tubular grafts to collapseat least partially. This is because, when the tube is curved for anyreason, the external diameter of the curve is necessarily longer thanthe internal, and the excess graft material on the internal diameter ofthe curve kinks into the lumen, thereby narrowing or even closing itcompletely. This problem also arises in vascular grafts for repair of,for example, the popliteal artery because of the extreme bendingmovements which are imparted to this artery during knee flexion.

Furthermore once a graft has been introduced into an artery by thesurgeon and located at the correct position, it is necessary to ensurethat it is reliably held at such position.

Some devices in use to date are based upon the combination of a stentwith a graft, a stent being a relatively rigid metallic cylinder withhighly fenestrated walls. This produces a strong implant but one whichis relatively inflexible. A frequent complication of arterial disease isthe development of highly tortuous vessels through which it is verydifficult to pass substantially rigid graft stents.

Most graft stents require the inflation of a balloon inside them toexpand the graft to fit within the blood vessel although self expandingdesigns have been recently introduced.

Most existing designs involve the use of a preformed stent which usuallyinvolves expensive construction techniques such as laser cutting andplasma welding.

In attaching the preformed stent to the graft, current devices usuallyinvolve multiple individual stitches around the stent and attached tothe graft. These stitches are necessarily attached by hand in a costlyand time consuming process.

A further problem with the current designs, arising from the substantialstent components, is the difficulty in designing bifurcated grafts whichcan be used at, for instance, the aorto-iliac bifurcation.

A further problem associated with long graft stents, particularly in thearteries of the lower limb, is irritation of the arteries arising fromtrauma of insertion and the longer term presence of the syntheticmaterial.

SUMMARY OF THE INVENTION

The present invention seek to provide an improved reinforced graft andmethod of making such a graft.

According to an aspect of the present invention, there is provided agraft including a sheet of flexible material, a plurality ofreinforcement elements extending transversely relative to a longitudinaldirection of the sheet of material, the reinforcement elements beingspaced from one another in the longitudinal direction, wherein at leastsome of the plurality of reinforcement elements are formed from acontinuous wire.

Advantageously, the sheet of material is formed as a tube with thereinforcement elements extending annularly around the tube.

The reinforcement elements are preferably compressible radially relativeto the tube.

When the graft is formed into its in-use shape, the reinforcing elementsare preferably pre-stressed. This enables the use of reinforcementelements which are more deformable than prior art devices.

According to another aspect of the present invention, there is provideda graft including at least one radio-opaque marker embroidered onto thegraft. Advantageously, the marker provides an indication of the part ofthe graft to which the marker is embroidered. For example, the markercould denote an “L”, “R”, “A” or “P” denoting, respectively, left,right, anterior and posterior. A plurality of opaque markers could beprovided on the graft.

It will be apparent that an embroidered marker could also be provided ona stent by providing embroiderable material on the stent.

According to another aspect of the present invention there is provided agraft or stent including at one extremity thereof a plurality offlexible members extending in a longitudinal direction of the graft orstent from an annular perimeter thereof, an annulus being provided at afree extremity of the flexible members, the flexible members beingdeformable substantially to a point to provide a flexible neck aboutwhich the annulus can rotate. This structure can provide a front guideto the graft or stent considerably facilitating insertion of the graftor stent into, for example, an artery, and greatly improving fixation inhighly tortuous vessels.

Preferably, the elongate members provide a flow path into the graft orstent.

In the preferred embodiment, the elongate members are provided withbarbs at their extremities remote from the graft or stent, for fixingthe graft or stent into, for example, an artery. Alternatively, separatebarbs may be provided on the annulus.

According to another aspect of the present invention, there is provideda method of forming a reinforced graft, including providing a sheet ofmaterial, a plurality of reinforcement elements in substantially flatconfiguration, sewing the reinforced elements to the fabric, forming thefabric into a substantially tubular shape.

This method enables the graft to be produced by conventional sewingmachines.

Preferably, the method includes a step of sewing guides over thereinforcement elements, moving the reinforcement elements into theircorrect position on the sheet of material, and then sewing thereinforcement elements into substantially fixed positions on the sheetof material.

Advantageously, the reinforcement elements are sewn loosely onto thesheet of material. For example, spaced stitches could be used to enableslight buckling of the material between stitches during compression ofthe graft. Alternatively, stitches which have a stitch width of 2 to 9times the width of the reinforcement elements could be used.

Advantageously, a reduced friction coated yarn is used to enable somemovement of the reinforcement elements relative to the sheet ofmaterial, particularly on compression of the finished graft.

In the preferred embodiment, the reinforcement elements are provided bya single wire sewn into a ladder of substantially straight portionsconnected by substantially U-shaped connecting portions. The connectingportions may be round or substantially square in shape.

Advantageously, the graft is formed so that connecting portions overlap.In the preferred embodiment overlapping connection portions are sewn toone another.

According to another aspect of the present invention, there is aprovided a method of forming a reinforced graft or stent in whichreinforcement elements are connected to a flexible fabric sheet by meansof a lock-stitch or chain-link.

According to another aspect of the present invention, there is provideda reinforced graft including a sheet of flexible material and aplurality of reinforcement elements, the reinforcement elements beingsubstantially parallel to the weft or warp of the fabric. Providingreinforcement elements substantially parallel to the weft or warp of thefabric provides a stable and substantially inelastic, non-expandablestructure. On the other hand, providing reinforcement elements atsubstantially 45° to the weft or warp provides a more elastic device.

The preferred embodiment can provide a reinforced graft which issufficiently flexible to allow it to be drawn through tortuous vesselsand which has sufficient radial stiffness to resist kinking andsubsequent collapse which would occlude the flow of blood through thegraft. It can be used for endovascular implantation in diseased arteriessuch as the aorta, carotid, iliac, femoral and popliteal arteries. Otherapplications of the device exist in vessels in the body such as veins,bile ducts, oesophagus, trachea etc.

Preferably, the reinforced graft is self expanding to the extent that itdoes not require a balloon for inflation.

Advantageously, the reinforced graft does not involve the separatemanufacture and attachment of a stent and can be manufactured simply andrelatively quickly. The simplicity of the preferred construction isintended to assist in the production of bifurcated, tapered andconnecting grafts.

It is preferred that the graft is sufficiently supple that it can beeverted so that when initially inserted, the proximal part of the graftcan be held and the distant part pulled through the proximal part sothat finally, the graft is everted end to end. This possibility reducesthe trauma of implanting long lengths of graft.

An example of a method of producing a reinforced graft comprises thesteps of attaching filamentary reinforcing material to a sheet offlexible graft material having opposite side edges so that thereinforcing material extends laterally over the sheet with respect tothe opposite side edges and is preferably attached along substantiallythe whole of its length to the sheet; forming the sheet into a tubehaving a longitudinal seam; and preferably securing together thereinforcing material on opposite sides of the longitudinal seam.

In this example, the reinforcing material can be very accurately andconveniently attached at the required places to the sheet when thelatter is laid out flat and before the sheet is formed into a tube, thusavoiding the complication of attaching the reinforcing material to apre-formed tube of graft material.

Preferably, the filamentary reinforcing material is attached to thesheet of flexible graft material so as to define a sinuous pattern ofthe reinforcing material in which a multiplicity of substantially linearregions extending laterally with respect to the sheet are joined bybends, and the bends at one side of the sinuous pattern are secured tocorresponding regions of the reinforcing material at the other side. Inthis way, spaced hoops of filamentary reinforcing material are providedwhich are secured to the tube, the hoops being spaced apart in thelongitudinal direction of extent of the tube. It will be understood thatthese hoops can be appropriately spaced apart so as to permit therequired flexibility of the tube to enable it to be bent around tortuousbends commonly encountered in the arteries of patients whilst stillsupporting the tube in such a way as to prevent kinking thereofexclusively in a localised region. Thus, when the tube is bent, it isconstrained to bend in a series of small kinks between the reinforcinghoops, and thereby able to follow curvatures encountered in practicewithout significant stenosis of the lumen.

In a particularly preferred embodiment, the bends are secured using tieswhich are not passed through the wall of the tube. This may be effectedsimply by passing the ties solely around the part of the filamentarymaterial to be joined together and knotting them.

The seam in the tube is preferably formed by securing the sheet alongthe side edges and then folding the portion of the tube in the region ofthe seam so that the fold is disposed on the outside of the tube.

Another example of a method of producing a reinforced graft comprisesthe steps of securing filamentary anchor material to flexible graftmaterial by attaching it to the graft material over a plurality ofspaced bends in the filamentary anchor material; and cutting thefilamentary material at regions between the bends so as to form amultiplicity of bristles or barbs of the filamentary material whichproject from the flexible graft material.

The bristles or barbs (hereinafter generally referred to simply asbristles) act as effective anchors which retain the graft in place inuse and may even be longer than the thickness of the wall of the arteryor other organ into which the graft is to be fitted.

Preferably, the flexible graft material is in the form of a sheet, andthis method includes the step of forming the sheet into a tube so thatthe filamentary anchor material is disposed on the outer surface of thetube. The cutting step may be performed before the tube is formed but ispreferably performed after.

Preferably, the bends are formed so that, although they may all face inthe same general direction relative to the direction of extent of thetube, some of the bristles extend from the bends at different anglesrelative to others in the direction of extent of the tube. This may beachieved by making some of the bends tighter than others.

The sheet of flexible graft material may be a woven or non-woven fabricformed e.g. of a suitable bio-compatible polymer such as abio-compatible polyester. A woven polyester microfibre (typically, 6–7μm diameter fibre) fabric is particularly preferred, which may be coatedfor example with gelatine or other material to enhance tissue in-growthor reduce thrombogenicity or permeability.

The filamentary material may be attached to one surface of the sheet bygluing or welding. However, it is preferred to effect the attachment bystitching, preferably using a computer controlled embroidery machine.Stitching may be effected over substantially the whole of the length ofthe filamentary reinforcing material which is fully secured to the sheetof flexible graft material and thus incapable of being displacedrelative to the sheet.

The filamentary material is preferably a material having super-elasticand/or shape-memory properties, e.g. a super-elastic, shape-memory alloysuch as a nickel-titanium alloy (e.g. Nitinol—50Ni/50Ti), and ispreferably also in the form of a wire. The wire may have a diameter ofabout 0.2 mm. However, it is within the scope of the present inventionfor the reinforcing material to be any suitable bio-compatible materialsuitable for implantation, for example nylon, polyester, silk,polyglycolic acid, polyactic acid, metal or alloy or any combinationthereof.

The preferred embodiment includes a combination of the features andmethods described herein. Thus, it is preferred for portions of thefilamentary reinforcing material used in the first method describedabove to define the plurality of bends provided in the second methoddescribed above. In such a case, the filamentary reinforcing material ischosen to be sufficiently rigid to impart the required anchor propertiesof the bristles formed from the bends.

A spring structure may be provided at one or both ends of the tubulargraft so as to assist in retention of the tubular graft against the wallof the artery in which the graft is in use located.

An example of reinforced graft comprises a tubular body formed offlexible graft material, and a filamentary reinforcing material securedto the graft material in a pattern such that the filamentary reinforcingmaterial extends around the tube and longitudinally thereof to allow thethus-reinforced tubular body to bend, wherein the pattern is definedwhilst the filamentary reinforcing material is being secured to thegraft material. This can be achieved before the tubular body is formedfrom a sheet of the graft material as described above, or it may beachieved by securing the filamentary reinforcing material to thepre-formed tubular body. The pattern may be a helical arrangement of thefilamentary reinforcing material around the tubular body, or it may be asinuous arrangement as described above. A sinuous arrangement whereopposed bends are overlapped and interdigitated (see below) can assistin imparting columnar strength to the tubular body.

Typically in the embodiments described herein the reinforcement does notconstitute a stand-alone stent.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are described below, by wayof example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a first embodiment of reinforced graftprior to rolling into a tubular shape;

FIG. 2 is a schematic diagram of a second embodiment of reinforced graftprior to rolling into a frusto-conical shape;

FIG. 3 a is a schematic diagram of part of the graft of FIG. 1 or FIG. 2when rolled into a tubular or frusto-conical shape;

FIG. 3 b is a schematic diagram similar to FIG. 3 a, showinginterdigitation of adjacent rung ends;

FIG. 4 is a schematic diagram of another embodiment of reinforced graftprior to rolling into a frusto-conical shape;

FIG. 5 is a schematic diagram of another embodiment of reinforced graftprior to rolling into a frusto-conical shape;

FIGS. 6 a and 6 b show two different methods of joining a reinforcedgraft into tubular form with both ends of a reinforcement rung opposingone another;

FIG. 7 is a schematic diagram showing a method of stitching areinforcement ladder lattice;

FIG. 8 is a schematic diagram showing the embodiment of reinforced graftof FIG. 1 in a flexed condition;

FIG. 9 is a schematic diagram of another embodiment of reinforced graftprior to rolling into a tubular shape;

FIG. 10 is a perspective view of another embodiment of reinforced graftshowing a wire stitched or woven through a sheet of graft fabricmaterial, prior to rolling;

FIG. 11 is a perspective view of another embodiment of reinforced graft;

FIGS. 12 to 22 are schematic diagrams of other embodiments of reinforcedgraft;

FIGS. 23 a to 23 f are schematic diagrams showing how barbs can beformed;

FIGS. 24 a and 24 b show another embodiment of reinforced graft; and

FIG. 25 is a schematic view of a reinforcement wire, barb orradio-opaque element sewn by a sewing machine to a fabric sheet.

DETAILED DESCRIPTION OF THE INVENTION

In the preferred embodiments described below, the graft comprises atextile polymer sheet which can be either flat or preformed into a tube.The sheet is subsequently reinforced by attaching one or more lengths offine wire to the material, either by stitching to the surface, threadingthrough pockets formed in the material, threading the wire through thebody of the material by weaving, braiding or knitting the wire into thebody of the material at the time of manufacture.

A convenient method of rapidly applying the wire to flat fabricdescribed in detail below, is by the use of a computer controlledembroidery machine which is used to form stitches over the wire andattach it to the fabric. This technique is restricted by availablemachinery to flat fabric which is subsequently rolled and joined to forma tube.

Alternative methods of construction allow the wire to be attached totubular devices, obviating the need for a join along the length of thedevice. Such joins have been implicated in longer term failures of someimplants.

The pattern in which the wire is laid on the fabric is important forachieving satisfactory mechanical characteristics. The wire is arrangedto run approximately circumferentially around the graft, andapproximately perpendicular to the long axis of the device. The wire isplaced along the length of the graft and each approximatelycircumferential section can be connected to other circumferentialsections so that, in the limit, the entire graft can be reinforced by asingle wire.

The intervals between each successive approximately circumferential turnare significant for it is between these parts that the fabric of thegraft can produce small buckles, allowing the overall graft to be bentand folded without collapsing the cross-section.

Referring to FIG. 1, the embodiment of reinforced graft shown includes asheet of fabric 10 of the type used for grafts. Onto this sheet 10 islaid a wire 12 which is preferably pre-arranged in a substantially flatladder pattern in which the straight portions 14 of the wire 12 may lieeither perpendicular to the longitudinal axis of the sheet 10 or at aslight angle to the normal to this axis.

The embodiment as shown in FIG. 1 is in use rolled into a tube such thatthe opposed rounded ends 16, 18 of the wire ladder 12 become locatedadjacent to one another. When the straight portions 14 of the wire lieperpendicular to the longitudinal axis of the sheet 10, the rounded ends16, 18 of the wire 12 interdigitate, as can be seen in FIGS. 3 a and 3b. This is described in further detail below.

On the other hand, when the straight portions 14 of the wire ladder 12are disposed at the appropriate angle to the perpendicular, the opposingrounded ends 16, 18 can be made to oppose or overlap one another, in themanner shown in FIGS. 6 a and 6 b, also described in further detailbelow.

FIG. 2 shows another embodiment of reinforced graft which includes asheet of graft material 20 which tapers from one end to the other in alongitudinal direction of the sheet 20 and a wire 22 of reinforcementmaterial configured in ladder-type fashion and which tapers in a similarmanner to the sheet 20.

The straight portions 24 of the reinforcement wire 22 can lieperpendicular to the longitudinal axis of the sheet 20 or at a slightangle thereto, in a similar manner to the embodiment of FIG. 1, so as toproduce the effects shown in FIGS. 3 a, 3 b, 6 a and 6 b.

FIG. 4 shows an embodiment of reinforced graft similar to that of FIG.2, in which the straight portions 24′ lie perpendicular to thelongitudinal axis of the sheet 20′ and in which at the wide end of thesheet 20′ there is provided a portion 30 of wire 20′ in which theindividual “rungs” have a much tighter pitch. This produces a stifferopening into the graft.

In the embodiment of FIG. 5, the reinforcing wire 32 is embroidered ontothe sheet material 40 as a sinuous pattern which extends over the lengthof the sheet 40 between the spring elements provided by the wire 32. Thesinuous pattern comprises a multiplicity of linear regions 34 which aremutually approximately parallel and which extend laterally of the sheet40 between the side edges of the sheet. The spacing between these linearregions 34 is greater in the upper wider part of the sheet material 40than in the narrower part. Adjacent linear regions 34 are joinedtogether alternately by semi-circular bends 36, 38 disposed adjacent theside edges of the sheet 40.

When the sheet 40 having the reinforcement wire embroidered thereon isbent to form a tube, the wire 32, as in the embodiments of FIGS. 1, 2and 4, is on the outside of the tube. The now-adjacent side edges of thesheet are stitched together to form a seam which is folded so as to lieinside or outside the tube so that adjacent bends 16, 18 on oppositesides of the seam can be secured together by knotting using ties.

Thus, in this embodiment, the linear regions 34 in the completed tubedefine a multiplicity of hoops around the tubular graft. These hoops arespaced apart longitudinally of the direction of extent of the tubulargraft and thus allow the latter to be bent in a controlled mannerwithout undue kinking at any specific location, thereby mitigating therisk of significant stenosis in use. The end of the tubular graftcorresponding to the lower region illustrated in FIG. 5 is of smallerdiameter and retains, in this example, a similar ratio of hoop spacingto graft diameter.

The pitch of the sinuous pattern is varied longitudinally of the sheet40 so that the pitch is greatest in the section of the graft 34 that isto be subjected to the greatest degree of curvature. In section 42 thereis a high density pitch to create a collar to hold the neck of the graftfully open and in firm contact with an artery wall. Section 44 is leftunreinforced to provide an area for fixation of the graft to the arterywall with an additional fixation device (not shown).

Section 46 is of low density pitch where the graft is intended totraverse a relatively straight path through the centre of an aneurysm.Section 48 is a transition section with medium density pitch to avoidkinking at the transition to section 50 which is of a high densitypitch. At section 50, the graft is required to pass through the mosttortuous section of a common lilac artery. Section 52 is of mediumdensity pitch to coincide with that portion of the graft which isintended to lie in the region of the artery which straightens into theexternal lilac artery. The optimum pitch for any section of the graft isa function of the expected degree of curvature and the diameter at thatsection.

The fabric used for the graft is standard fabric use in the art, forexample micro-fine woven polyester. The wire may be of any suitablefilamentary material, such as a nickel/titanium shape-memory alloy (SMA)material, a super-elastic shape-memory alloy material such as that soldas Nitinol. Substances other than shape-memory alloy could be used, therequirements for preferred embodiment being a material which can bedeformed to assist insertion of the graft into an artery or other vesselor conduit and which can subsequently return to its un-deformed shape soas to open the graft once inserted.

The advantage of shape-memory alloy is that the graft can be compressedeasily for insertion and then allowed to expand to its memorised shapeas it heats up to body temperature.

For this purpose, the preferred embodiment uses an equiatomicnickel/titanium alloy which is triggered at about blood temperature andwhich in a fully annealed condition is highly ductile. This condition isnot typically used in medical devices which commonly employ “superelastic” material (sometimes referred to stress-induced martensitic(SIM) alloy). The use of a ductile alloy greatly eases handling duringmanufacture. Preferably, the ductile wire is mechanically polishedbefore integration into the graft.

The preferred diameter of the wire is 0.2 mm to 0.3 mm, although anydiameter between 0.15 mm and 0.5 mm can be used.

If the graft is provided with barbs, these need not be of shape-memoryalloy.

The thread used to stitch the reinforcement wire to the fabric sheet ispreferably a reduced friction coated yarn.

The preferred method of producing the graft is now described, withreference to FIG. 7 in combination with FIGS. 3 a, 3 b, 6 a and 6 b.

As has been described with reference to the embodiments of FIGS. 1, 2, 4and 5, the sheet material of appropriate shape is preferably laidsubstantially flat with a single wire of reinforcement material beinglaid on top of the sheet of fabric. For this purpose, the wire ispreferably produced in a substantially planar configuration and, as canbe seen in the Figures, can be said to have a sinuous or ladder pattern.

Referring to FIG. 7, a first stitch line 51 is produced close to oneedge of the wire ladder 12. Once this line of stitches is produced, thewire 12 can be moved laterally across the sheet 10 for correct location.Once located correctly, the curved ends 16, 18 of the wire are stitched53, prior to stitching of the substantially straight portions 14 of theladder rungs.

Usually, shaped-memory alloy wire is heat treated in the shape which isto be its final form. On cooling, the wire is ductile and easilydeformed but on warming to body temperature, the wire reverts to theform which it has been “taught”. In the preferred embodiment, however,no such “teaching” is involved, apart from the planar shape of the wireas originally supplied. It has been found in practice that on heatingthe wire, when attached to the graft in the manner described, the graftforms a desired rigid cylindrical shape without the need for precisetraining of the wire. Moreover, such formation of the tubular graftcauses it to be pre-stressed and therefore relatively stiffer than anun-stressed equivalent. This enables the use of wires of smallerdiameter.

The ratio of the spaces between ladder rungs to the diameter of thegraft is most preferably 1:3. A ratio of 1:2 has been found to work,with a ratio for the stiffer parts of the graft being preferably around1:9. It has been found that a ratio of ladder rungs to diameter of 1:20is also possible, sometimes benefiting from the use of a softer graftmaterial.

FIG. 7 shows straight portions 14 of the wire 12 being stitchedsubstantially continuously along their length. In order to allow forslight buckling of the graft to pass through catheters and to fitarterial curves, the stitches are preferably loose. This can be achievedby reducing stitch tension, increasing stitch size and/or using areduced friction coated yarn. The preferred embodiment uses an increasedstitch size and it has been found that a stitch size around three timesthe diameter of the wire is suitable although stitch sizes between sixto nine times the diameter of the wire have also been used.

Another feature which can lead to different graft characteristics is theorientation of the wire rungs relative of the weft or warp of thefabric. More specifically, when the straight portion 14 of the wire 12lie parallel to the weft or warp of the fabric sheet 10, the graftbecomes substantially stable. On the other hand, when the straightportions 14 of the wire 12 are oriented so as to lie at an angle, forexample 45°, to the weft or warp of the fabric sheet 10, the graftbecomes more deformable. Alternatively or additionally, the fabric sheet10 could be elasticated.

Stitching is preferably carried out by means of a computer controlledembroidery machine of the type particularly used to embroider insignia,badges and logos on uniforms, leisure wear and promotional garments.These machines have the advantage of being fast and providing reliablerepeatability.

It is also envisaged that with computer controlled embroidery and by thedesign of the graft of the preferred embodiment, it would be possible todesign specific grafts by CAD/CAM techniques, thereby considerablyfacilitating the production of custom implants.

However, manual stitching techniques can also be employed.

Once the reinforcement wire 12 is sewn to the fabric sheet 10, the sheet10 is then rolled along its longitudinal axis to form a tube, with theopposing curved ends 16, 18 of the wire 12 moving so as to be locatedadjacent one another. Once rolled, the longitudinal edges of the sheet10 are sewn together.

In FIGS. 3 b and 6 b, the edges of the sheet 10 are sewn such that thecurved ends 16, 18 of the wire 12 do not overlap one another. On theother hand, in the embodiments of FIGS. 3 a and 6 a, the edges of thesheet 10 are stitched so as to overlap one another and such that theends 16, 18 of the wire 12 also overlap.

In FIG. 3 a, the ends 16, 18 interdigitate, whilst in FIG. 6 a the ends16, 18 overlap in substantial alignment.

As will be apparent in FIG. 3 a, there are shown stitches 60, 62 whichstitch together the overlapping ends 16, 18 of the wire 12. Similarstitches will be provided in the example of FIG. 6 a. The advantage ofstitching 60, 62 in the manner shown is that this ensures the graft hasa substantially circular axial cross-section, with the stitches 60, 62preventing deformation from the circular shape. Without such stitching,the force produced in seeking to return the wire 12 to its substantiallyflat shape causes the tube to adopt a pear-shape.

The examples of join shown in FIGS. 3 b and 6 b can be arrangednevertheless to ensure that the graft is substantially circular in axialcross-section by, for example, bending the ends 16, 18 out of the planarconfiguration at a radius which would be equivalent to the radius of thegraft when rolled into its tubular form.

One feature of having the ends 16, 18 of the wire 12 overlap is thatalong the seam the graft exhibits a certain degree of longitudinalstiffness. When the ends 16, 18 do not overlap (for example abut oneanother) this longitudinal stiffness is not apparent. This canfacilitate deployments which involve inversion of the section of thegraft and can also facilitate an intra-operative adjustment in length ofthe graft by allowing the graft material between pairs of rungs to varybetween being taut and buckled. An example of graft could have the loopsinterdigitating for the main body of the device and overlapping for theends where the artery wall provides more natural support to the circularcross-section required from the graft and where an optional adjustmentin length may be desirable.

Once set in its tubular form, the graft is substantially ready for use.Other elements may be attached to the graft, as described below.

In the preferred embodiments, the reinforcing wire 12 is located ondifferent sides of the fabric sheet 10. More specifically, in theexamples described above, the reinforcement wire 12 has been located ona single side of the fabric sheet 10, in use to be either on the outsideor on the inside of the fabric tube once rolled.

However, it is sometimes preferred to have at some portions of the graftreinforcement wires on the outside of the graft and at other portionsreinforcement wires on the inside of the graft. This can be achieved byusing separate wires or by using a common wire which, during theplacement process, it pushed through the fabric sheet 10 so as to belocated, respectively, on one and on the other side of the sheet 10.Stitching can be achieved equally well with the wire on both sides ofthe fabric sheet 10.

A preferred embodiment has the wire on the inside of the graft at theends of the graft, where optimum seal is required between the graft andthe wall of an artery. In the centre portion of the graft, where it isdesirable to minimise the potential disruption to the blood flow andmaximise the anti-kinking support to the graft material, the wire islocated on the outside of the graft tube.

In dependence upon the manner of manufacture of the graft, it may beadvantageous to form the graft inside out, the thus formed graft thenbeing everted to its correct configuration. Similarly, eversion could bedeployed to facilitate insertion of the graft into an artery.

FIG. 8 is a cross-sectional view of the embodiment of graft of FIG. 1which is bent into curved fashion. It can be seen that the graft sheet10 is allowed to buckle 70 slightly so as to allow the graft to curve.

In the preferred embodiment, the entire graft can be wrapped around itsown diameter in its longitudinal extent performing a tight curve withoutcollapse or significant kinking.

Once the graft has been formed, it is then inserted into the artery ofthe patient in a manner known in the art.

In the embodiments which utilise a shape-memory alloy, the graft will benormally cooled to below the critical (trigger) temperature of theshape-memory alloy and compressed radially before it is inserted by thesurgeon into position. This gives a compacted graft which may have afolded, star-like cross section which opens out after insertion into thebody and heating to above the trigger temperature of the shape-memoryalloy to return to a generally circular cross-section. When deployedwithin the arterial system, the graft should be sufficiently reduced soas not to over-expand, which could potentially damage the artery, butmay have sufficient ability to increase in diameter to allow for anyincrease in size of the aneurysm after insertion. The graft may belocated in a catheter or sleeve for insertion along the arterial systemto the correct position. The provision of such a catheter or sleeveprevents expansion of the graft before it has been located in thedesired position.

Typically, the graft will be introduced into the patient by means of acatheter which is cooled to allow the reinforcing wire of the implant toremain below body temperature and therefore ductile. The implant isdrawn through the catheter to the implantation site by means of a pusherwire which is attached to the graft by means of wire or filamentaryloops.

It is desirable to have a means of controlled release of the attachmentloops so that for instance, a second pusher wire can be introduced nextto the first pusher wire, and is attached to the proximal end of thegraft. By pushing the second wire and puling the first wire, the implantcan be everted.

Ideally, the entrance to the catheter is of an oval or stellate form sothat the implant is crushed in a regular shape to have a smallerexternal diameter during implantation. Upon exiting the catheter intothe blood stream the SMA wire of the graft is warmed and adopts astraighter shape similar to that originally formed in the implant.

Before describing other elements which can be formed on the graft of theembodiments described above, further embodiments of graft are described.

With reference to FIG. 9, a wire 102 is located on a sheet of fabric 100such that some portions 104 of the wire are located above the sheet 100,as seen in FIG. 9 and other portions 106 are located below the sheet100. This is achieved by sequential feeding of one end of the wire 102into and out of the sheet 100 to provide the pattern shown. The specificpattern shown in FIG. 9 provides two stiffness lines in the longitudinaldirection of the graft. In FIG. 10, the wire 102 can be seen threadedinto and out of sheet 100′.

In FIG. 11, the sheet of graft fabric 110 is provided with a pluralityof transversely-extending pockets 112 through which a wire 114 can bethreaded. The pockets 112 provide the wire 114 its required shape.

In FIG. 12, a woven polyester microfibre sheet S has opposite side edgesS1 and S2 tapering inwardly from top to bottom as viewed in FIG. 12 andis shaped so as to enable a tubular graft to be formed which tapers froma relatively wide diameter at one end to a relatively narrow diameter atthe other end. The precise shape and size of the sheet S is determinedaccording to the particular configuration of the aortic artery intowhich the tubular graft is to be fitted.

The sheet S has filamentary reinforcing material F stitched to onesurface thereof by means of a computer controlled embroidery machine.The filamentary reinforcing material F is preferably a single filamentwhich is secured to the sheet S so as to define a multiplicity ofzig-zag patterns extending laterally of the sheet S between the sideedges S1 and S2. The zig-zag patterns are spaced apart longitudinally ofthe sheet S over substantially the whole of the length of the latter.

The embroidery operation to form the filamentary reinforcing material Fto the required shape also defines a series of loops L which projectlaterally beyond the side edge S1 of the sheet S. The sheet S is alsosubjected to a further embroidery operation in which a length of springmaterial M is used to form spring elements at the top and bottom. Eachof these springs elements is defined by a zig-zag pattern extendingacross the sheet S. In forming the zig-zag pattern, the filamentaryspring material is looped over at locations typically indicated byreference numerals 1 and 2.

Extending along the side edges S1 and S2 of the sheet are reinforcements3 and 4 which provide longitudinal stiff pillars imparting lengthwisestiffness and column strength to the graft to prevent it buckling duringinsertion. The pillars 3 are defined by portions of the spring materialM, while the pillar 4 is provided by regions of the filamentaryreinforcing material F.

After the structure described above with reference to FIG. 12 has beenproduced, the sheet material S is folded into tubular form with the sideedges S1 and S2 adjacent. These are then stitched together to form aseam and the loops L are secured by suture material to the now-adjacentopposite portions of the respective zig-zag patterns embroidered on tothe sheet material S.

The loops at 1 and 2 enhance the properties of the spring.

In FIG. 13, the graft is formed with ties 214 which are engagable withrespective loops 215 when sheet material S is formed into a tubularshape. In this embodiment, further longitudinal stiffeners 216 and 217are provided approximately midway between side edges S1 and S2. The ties214 are knotted to the respective loops 215 to retain the tubular formof the graft.

In FIG. 14, elementary spring material M is embroidered onto sheet S toform a series of bends 218 arranged in a fish scale pattern.

In FIG. 15, there is illustrated another pattern for forming the springelements at opposite ends of the graft using elongate spring material M.The arrangement is similar to that of FIG. 12, but the path of theembroidery machine is different.

FIG. 16 shows an arrangement also similar to that of FIG. 12. Pattern224 of the filamentary reinforcing material F is intermittent down thelength of the graft to provide more flexibility. Retention hooks areshown at 225 which assist in retaining the graft in position in theartery in which it is fitted in use. The spring elements at the top andbottom of the graft are defined by the spring material M, and the smallloops 1 and 2 are used to assist attachment of these to the sheet S.

FIGS. 17 to 22 show alternative patterns of the filamentary reinforcingmaterial which can also be stitched at selected locations using acomputer-aided embroidery machine onto the sheet S in order to providecolumnar stiffness combined with radial springiness to hold the lumenopen. At the top and bottom of the sheet S are shown looped hook wirearrangements acting to secure the graft in place.

The materials used for reinforcing in the above described embodimentsmay be any bio-compatible materials suitable for implantation, includingnylon, polyester, silk, polyglycolic acid, polylactic acid and metallicwire. The use of monofilament polyester and super-elastic orshape-memory metals alone or in combination is preferred. The use of asuper elastic, shape-memory alloy such as Nitinol allows the device tobe self-expanding and does not require the use of an additional device(such as a balloon catheter) to expand the generally cylindrical shapefrom a compressed condition to an extended condition.

Additional elements for the embodiments of graft described above are nowmentioned.

The device may be retained in the required position within the artery byuse of a multiplicity of retaining bristles or barbs formed fromsuitably rigid metallic or polymeric material. These barbs may bearranged to protrude a sufficient distance from the external surface ofthe tubular graft and when provided in sufficient numbers they willengage within or through the wall of the blood vessel such as to resistmovement of the graft under the force exerted by the flow of blood therethrough.

FIGS. 23 a to 23 f show various arrangements for producing bristles orbarbs on the outer surface of the graft at the upstream end thereofrelative to the direction of flow of blood therethrough. In FIG. 23 ashape-memory alloy wire W is attached to the sheet S (not illustrated inFIG. 23) by stitching the wire using a computer-controlled embroideringmachine over spaced bends W1 in the wire W. These spaced bends W1 arespaced apart around the periphery of the tubular graft and areinterconnected by intervening regions W2 which are left free, i.e. arenot attached by stitching to the sheet S.

Cutting of the wire W at these regions W2 as indicated schematically bythe scissors in FIG. 23 a results in the formation B in the completedgraft. These bristles B point generally in the direction of blood flowthrough the graft and act as barbs which dig into the wall of the arteryto prevent the flow of blood in the aorta, or other forces such aspatient movement, from dislodging the graft from its placed position.

As can be seen from FIG. 23 b at 180° bend W1 will result in thebristles B projecting parallel to the longitudinal axis of the graft.This is optimum for resisting the main force of the blood flow.

As indicated in FIG. 23 c, bends W1 with an angle of less than 180° willresult in the bristles B extending at an angle to the longitudinal axisof the graft. This configuration is optimum for resisting torsionalforces acting on the graft.

As shown in FIG. 23 b 180° Bends W1 may alternate with bends of an angleless than 180° to produce combined effects.

As shown in FIG. 23 e there are three rows of barbs arranged in astaggered formation on the external surface of the graft such that thereis an optimal variation in the direction of the extent of the bristles Bto ensure that a mechanical lock with the wall of the artery is ensuredirrespective of the lack of uniformity that is commonly found inarteries.

In FIG. 23 f there is shown an arrangement where the wire W forming thebends W1 overlies a circumferential wire CW so that the latter isdisposed in the region of the junction between the bends W1 and theintervening regions W2. The result of this is that, after cutting at theregions W2, the bristles B protrude at a definite angle from the surfaceof the sheet S.

Additionally, further stitching may be utilised in the region where thewire W crosses over the circumferential wire CW so as to provideadditional anchorage or the bristles B at the points where thesebristles protrude from the wall of the tubular graft.

The preferred embodiments also provide for the attachment ofradio-opaque elements to the sheet of graft material. The elements arepossibly embroidered onto the sheet of fabric. The preferredradio-opaque element is a fine wire embroidered in a pattern to providecalibrated deformations along its length to provide a radio-opaquelength measurement along the longitudinal axis of the graft.

In an alternative embodiment, the radio-opaque elements provideindications of “left”, “right”, “anterior” and/or “posterior” and may,for example, be in the form of letters designating the first letter ofeach of these position terms.

In the case of a radio-opaque element, this could be a tantalum or otherhigh molecular number element (opaque) wire embroidered onto the sheetof fabric. Alternatively, the radio-opaque markers could be aradio-opaque ink printed on the fabric, pellets or a sheet of materialembroidered over the fabric sheet.

The opaque markers, and indeed the reinforcement wire 15″ itself or thebarbs could be provided on a sewing machine bobbin to be placed on thefabric sheet 10″ in a lock-stitch 15, as shown in FIG. 25.

In FIG. 24 a is provided an example of graft 300 formed in accordancewith any of the above-described embodiments and which has at one of itsends 302 a region 306 not covered by graft fabric 304. Beyond region306, there is a small annulus 308 of graft material. Between the annulus308 and the graft 300 there is provided a plurality of struts 310 ofshape-memory alloy connecting the graft 300 to the annulus 308. Thelocation 306 allows the graft 300 to be placed between two arteries.

The advantage of the structure shown in FIG. 24 a is that the annulus308 can be rotated, for example in the direction shown in the arrow 312,such that the structure 310 twists to a neck 314 as seen in FIG. 24 b. Aloose connection between the struts 310 and the annulus 308 assists inthis generation of the neck 314. In its twisted shape, the neck 314 canbe tied providing a very flexible leading end of the graft 300 by meansof the mobility of the annulus 308.

It can be seen in FIGS. 24 a and 24 b that the struts 310 also providebarbs 320.

In all the described embodiments, the barbs could be separate elementsstitched to the fabric sheet. The advantage of this is that there is norisk of weld fractures.

One practical use of the graft of FIGS. 20 a and 20 b is as asupra-renal fixation element.

It is envisaged that any of the grafts described herein can be used asan occluder by providing a fabric cover over one of the open ends of thetubular graft. Alternatively, the graft could be used as a platform forthe deployment of an artificial valve.

The described embodiments facilitate a significant increase in diameterof the graft over a very short axial length while preserving all thedesirable attributed of the graft. An embodiment of a graft with such adramatic change in diameter is for the endoluminal treatment of anabdominal aortic aneurysm with shape of an “Ali Baba's Basket”. In thissituation there is essentially no neck to anchor onto between theaneurysm and the renal arteries. The graft can be manufactured anddeployed such that it is an optimal fit at the point where the renalarteries branch off and then flares out to match the shape of the top ofthe aneurysm. This graft would be anchored in position primarily with asupra-renal fixation element.

The stitching used to attach the preform to the graft fabric can bevaried in order to optimise mechanical characteristics. Stitches may betriangular or square in order to control the contact area betweenpreform and stitching thread.

The graft may be used in conjunction with a self-sealing element such asan occlusion device. This may be on normal applications of the graft orwhen used as an occlusion device in conjunction with an occlusionbarrier or when used as an artificial vein.

The pattern of preform can be selected in order to create sections alongthe length of the graft that can vary from being totally flexible tototally supported. In an embodiment used as an occlusion device, twohighly supported sections are linked by a highly flexible section whichallows the supported sections to deploy perpendicular to the long axisof the vessel irrespective if the tortuosity of the vessel.

The occlusion barrier may be created with a preformed ring of SMA or acircular or spiral pattern that may be embroidered wire or an attachedpreform in order to improve the seal in a vessel with an irregular crosssection.

In all the above-describe embodiments, the fabric seam could be producedby sewing, welding, thermal bonding and by use of adhesives.

1. A method for forming a non-expandable reinforced graft including thesteps of a. providing a sheet of flexible graft material having opposedside edges; b. attaching filamentary reinforcement material to thesheet, wherein the filamentary reinforcement material is provided in apattern including regions: (1) extending at least substantiallytransversely towards a first one of the side edges of the sheet, (2)changing direction by approximately 180°, and (3) extending at leastsubstantially transversely towards the second one of the side edges ofthe sheet, wherein: i. the pattern is repeated to run at leastsubstantially longitudinally with respect to the side edges of thesheet; and ii. the filamentary reinforcement material is attached intosubstantially fixed positions on the sheet, whereby the reinforcementmaterial is not displaceable relative to the sheet; c. forming the sheetinto an at least substantially tubular shape by bringing together theside edges to form a longitudinal seam.
 2. The method of claim 1 whereinthe regions in which the filamentary reinforcement material changedirection by approximately 180° are U-shaped.
 3. The method of claim 1wherein the reinforcement material is formed from a single wire.
 4. Themethod of claim 1 wherein the sheet of flexible graft material is formedinto the tubular shape prior to having the filamentary reinforcementmaterial attached.
 5. The method of claim 1 wherein the side edges arebrought together in such a manner that the regions in which thefilamentary reinforcement material change direction by approximately180° overlap.
 6. The method of claim 5 wherein the overlapping regionsin which the filamentary reinforcement material change direction byapproximately 180° are sewn to one another.
 7. The method of claim 1wherein the filamentary reinforcement material is attached to the sheetin such a manner that the regions in which the filamentary reinforcementmaterial change direction by approximately 180° overlap.
 8. The methodof claim 7 wherein the overlapping regions in which the filamentaryreinforcement material change direction by approximately 180° are sewnto one another.
 9. The method of claim 1 wherein the filamentaryreinforcement material is prestressed.
 10. A method for forming anon-expandable reinforced graft including the steps of: a. providing asheet of flexible graft material having opposed side edges; b. attachingfilamentary reinforcement material into substantially fixed positions onthe sheet, whereby the reinforcement material is not displaceablerelative to the sheet, wherein the filamentary reinforcement material isprovided in a pattern including regions: (1) extending at leastsubstantially transversely towards a first one of the side edges of thesheet, (2) changing direction by approximately 180° to form a bend inthe reinforcement material, (3) extending at least substantiallytransversely towards the second one of the side edges of the sheet, (4)changing direction by approximately 180° to form another bend, whereinthe pattern is repeated to run at least substantially longitudinallywith respect to the side edges of the sheet; and c. forming the sheetinto an at least substantially tubular shape by bringing together theside edges to form a longitudinal seam.
 11. A method as claimed in claim10, wherein the sheet is formed into said tubular shape in such a waythat bends on either side of the longitudinal seam overlap, oppose,interdigitate or abut.
 12. A method as claimed in claim 10, whereinbends at one side of the longitudinal seam are secured to correspondingbends at the other side.
 13. The method of claim 10 wherein thefilamentary reinforcement material is prestressed.
 14. A method forforming a non-expandable reinforced graft including the steps of a.providing a sheet of flexible graft material having opposed side edges;b. attaching filamentary reinforcement material to the sheet, whereinthe filamentary reinforcement material is provided in a patternincluding regions: (1) extending at least substantially transverselytowards a first one of the side edges of the sheet, (2) changingdirection by approximately 180°, and (3) extending at leastsubstantially transversely towards the second one of the side edges ofthe sheet, wherein: i. the pattern is repeated to run at leastsubstantially longitudinally with respect to the side edges of thesheet; and ii. the regions in which the filamentary reinforcementmaterial change direction by approximately 180° overlap; c. forming thesheet into an at least substantially tubular shape by bringing togetherthe side edges to form a longitudinal seam; and d. sewing to each otherthe overlapping regions in which the filamentary reinforcement materialchange direction by approximately 180°.
 15. The method of claim 14wherein the regions in which the filamentary reinforcement materialchange direction by approximately 180° are U-shaped.
 16. The method ofclaim 14 wherein the reinforcement material is formed from a singlewire.
 17. The method of claim 14 wherein the sheet of flexible graftmaterial is formed into the tubular shape prior to having thefilamentary reinforcement material attached.
 18. The method of claim 14wherein the filamentary reinforcement material is attached intosubstantially fixed positions on the sheet, whereby the reinforcementmaterial is not displaceable relative to the sheet.
 19. The method ofclaim 14 wherein the filamentary reinforcement material is prestressed.20. A method for forming a non-expandable reinforced graft including thesteps of: a. providing a sheet of flexible graft material having opposedside edges; b. attaching filamentary reinforcement material to thesheet, wherein the filamentary reinforcement material is provided in apattern including regions: (1) extending at least substantiallytransversely towards a first one of the side edges of the sheet, (2)changing direction by approximately 180° to form a bend in thereinforcement material, (3) extending at least substantiallytransversely towards the second one of the side edges of the sheet, (4)changing direction by approximately 180° to form another bend, whereinthe pattern is repeated to run at least substantially longitudinallywith respect to the side edges of the sheet; and c. forming the sheetinto an at least substantially tubular shape by bringing together theside edges to form a longitudinal seam, wherein bends at one side of thelongitudinal seam are secured to corresponding bends at the other side.21. A method as claimed in claim 20, wherein the sheet is formed intosaid tubular shape in such a way that bends on either side of thelongitudinal seam overlap, oppose, interdigitate or abut.
 22. The methodof claim 20 wherein the filamentary reinforcement material is attachedinto substantially fixed positions on the sheet, whereby thereinforcement material is not displaceable relative to the sheet. 23.The method of claim 20 wherein the filamentary reinforcement material isprestressed.